ABSTRACT
We present the dispersion relation of guided-mode resonances in non-dissipative dielectric diffraction gratings, both for s-polarized (TE mode) and p-polarized (TM mode) incident waves. We present a simple approximate theory as well as a rigorous calculation within the so-called coupled-wave theory. We discuss the dependence of the positions and the lifetimes of the resonances on the thickness of the gratings and on the strength of its modulation. We find that the diffraction efficiency of the different orders show peaks at different Bragg orders.
ABSTRACT
Using simple considerations of causal electrodynamics we analyze the occurrence of superluminal transmission of light pulses through optically opaque barriers. We find that the phenomenon appears whenever the main frequency components of the pulse are confined to frequency regions where the presence of the barrier decreases the density of states of the electromagnetic modes of the system. We also show that these frequency regions correspond to the transmission gaps of sufficiently wide barriers. We discuss a simple theory for the density of states of the barrier system and compare the results of such a theory with exact numerical calculations.
ABSTRACT
The surface tension and the bending rigidity of a planar liquid-vapor interface in the presence of vanishing gravity are analyzed using the renormalization group. Based on the density functional theory of inhomogeneous fluids, we show that a term, quartic in the density fluctuations, can be added to the classical capillary-wave model so that a renormalization-group calculation can be performed. By comparing the outcome of such a calculation with rigorous results relating the direct correlation function with surface tension and bending rigidity, we find the scaling dependence of the latter on gravity. The results agree with the expected fact that the interface should become unstable as gravity vanishes.